Composite cable for conducting electricity



Jan. 22, 1957 v. B. NOLAN COMPOSITE CABLE FOR CONDUCTING ELECTRICITY Filed Nov. 19, 1955 kA/UQLEO SUQFA CE IN VEN TOR. VINCENT B. NOLAN United States Patent C(EMPOSITE CABLE FOR CONDUCTING ELECTRICITY Vincent B. Nolan, Miami, Fla., assignor to Bethea Company, Inc., a corporation of Alabama Application November 19, 1953, Serial No. 393,079

7 Claims. (Cl. 174-128) This invention relates to a composite cable and the process of constructing the same and more particularly to a cable for conducting electric currents and embodying a high tensile strength core element surrounded by a number of electrically conductive wires.

One object of my invention is to provide a composite aluminum-steel cable having associated therewith improved means increasing the effective coefiicient of friction between the steel core and the aluminum strands, thus preventing slippage therebetween when the cable is clamped to supporting structures under tension.

A further object of my invention is to provide an aluminum-steel cable of the character designated in which the means preventing slippage between the steel core and the aluminum strands is applied along the entire length thereof at the time the composite cable is formed, thus permitting the cable to be clamped at any point without the necessity of special preparations at the time the cable is attached to a supporting structure.

A still further object of my invention is to provide a cable of the character designated in which the physical strength thereof is not materially diminished by the incorporation of my improved means preventing slippage between its composite elements.

As is well known in the art to which my invention relates, aluminum-steel cables have become one of the predominant means for conducting high voltage electric current. The cable is usually made up of a high tensile steel core wire around which is stranded a number of aluminum wires for conducting the electric current. The reason for this construction is that aluminum is a good conductor of electricity but has inferior strength characteristics and the steel core is employed to give the necessary strength to the composite cable. T o prevent electrolytic action between the steel core and the aluminum wire, the steel core is usually galvanized. This type of cable is satisfactory under ordinary operating conditions, but difficulties have been encountered in coastal and industrial areas due to the fact that very small amounts of salt or other chemicals in the air tend to cause the galvanizing on the steel core to break down. Electrolytic action may then take place, causing destruction of the cable. In order to overcome this difliculty, it has become the practice to coat the galvanized steel core with a non-oxidizing heavy grease.

While the heavy grease protects the galvanized steel core for a long period of time, it tends to permit relative slippage between the aluminum wires and the steel core when the cable is clamped to a supporting structure under tension. Accordingly, it is very diflicult for the steel core to carry the full tension of the cable because the load must be transferred from the steel core, through the aluminum strands, to the means clamping the cable to the supporting structure. This is particularly true at any place where a dead end is required, such as at the end of a power line or points where the line turns at sharp angles. The holding power of the clamping means thus depends upon the clamping pressure developed by the 2,778,870 Patented Jan. 22, 1957 2 clamp and the effective coefficient of friction between the clamp and the aluminum strands and between the aluminum strands and the steel core.

Heretofore, in order to secure effectively an aluminumsteel cable coated with such grease to its supporting structure, the cable had to be cut, the aluminum strands unraveled and the steel core scarred by means of a small hand tool or coated with gritty material, such as Carborundum dust. The aluminum strands were then replaced and the clamping means applied. This preparation of the wire is time consuming and the cutting operation of the hand tool or the grit damages the galvanizing coat on the steel core. Also, the cutters on the hand tool must be very sharp in order to apply the required amount of force to scar the hard surface of the core. Such sharp cuts in the core cause it to become weakened due to the fact that points of stress concentration are created. The sharp edged grit particles also cause a similar weakening of the core.

Where the composite cable is not coated with grease it has been the practice to apply the clamping means without any special preparation of the cable. However, due to the fact that the low coefiicient of friction between the zinc coating on the core and the aluminum strands, the full strength of the composite cable has been realized only with great difficulty, if at all.

An alternate means for securing composite cables in place has been to cut the cable and trim back the aluminum strands to leave a length of the steel core exposed. The steel core and the portion of the cable covered by the aluminum strands were then clamped separately so that the full strength of the composite cable could be realized. This method is also time consuming, requires special equipment, and necessitates auxiliary connections or splices in order to re-establish a current path.

Briefly, my improved aluminum-steel cable construction comprises a steel core having a surface provided with relatively shallow knurls or serrations thereon for obtaining holding power by mechanical means in addition to the ordinary friction between the steel and aluminum Wires.

Composite cables embodying features of my invention are shown in the accompanying drawing forming a part of this application in which:

Fig. 1 is a perspective view thereof;

Fig. 2 is a sectional view taken along the line II-II of Fig. 1, and drawn to a larger scale;

Fig. 3 is a sectional View showing a modified form of cable construction; and,

Fig. 4 is a side elevational view showing a still further modified form of cable construction.

Referring now to the drawing for a better understanding of my invention, I show a cable 10 comprising a high tensile steel core wire 11 around which is stranded a number of aluminum wires 12 for conducting electric current. In order to obtain additional holding power between the outer surface of the steel core 11 and the inner surface of the aluminum wires 12, the outer surface of the steel core is knurled or otherwise deformed as at 13. The knurled surface is applied along the entire length of the steel core wire by rolling or other suitable means so as to form relatively shallow and rounded serrations on the surface thereof, thus eliminating fatigue failure caused by points of stress concentration.

After the knurled surface has been applied to the steel core 11, a protective coating of zinc is applied thereto in a manner well understood in the art. The aluminum wires 12 are then stranded around the core 11 to form the compo-site cable. If the cable is to be used in coastal areas or other areas where the galvanizing on the steel core may be broken down by chemical reactions, a heavy v 3 non-oxidizing grease is applied to the galvanized core before the aluminum wires are stranded around the same.

Referring to Fig. 3 I show a modified form of cable construction in which a plurality of steel core wires are provided with the knurled surface 13 and then galvanized separately in the manner described above. The cable comprises a central steel core wire 14 surrounded by an annular layer of steel wires 16. Surrounding the layer of steel wires 16 are annular layers of aluminum wires 17 and 18.

In Fig. 4 I show another form of cable construction embodying a steel core 19 surrounded by aluminum strands 21. The core 19 is slightly deformed along the outer surface thereof by varying the diameter of the wire as at 22. This shape is preferably applied to the wire as it is drawn by passing it through suitably formed rolls so as to form a plurality of annular depressions along the entire length thereof.

While I have described the steel core wires 11, 14, 16 and 19 as being galvanized, it will be apparent that other types of wires may be employed without the protective coating, such as stainless steel or the like. Also other arrangements of the core wires relative to the strands of aluminum Wire may be employed. It will also be apparent that the conducting wires may be formed of other materials, such as copper.

From the foregoing it will be seen that I have devised an improved composite cable and process for constructing the same in which slippage of the individual surrounding strands relative to the core wire is greatly minimized. By providing relatively shallow rounded deformations on the surface of the core, there is no fatigue failure due to points of stress concentration. Also the physical dimensions of my composite cable having a deformed outer surface on the core wire are substantially the same as those of an equivalent cable with a plain core wire. While my cable construction is adapted f" use with cables having a core which is not coated with heavy grease, it is particularly adapted for use with such cables that do have the protective grease coating applied to the core wire thereof.

While I have shown my invention in several forms, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various other changes and modifications without departing from the spirit thereof, and I desire, therefore, that only such limitations shall be placed thereupon as are specifically set forth in the appended claims.

What I claim is:

1. In a composite cable for conducting electricity, a high tensile strength core wire having relatively shallow and rounded serrations 0n the outer surface thereof, and a plurality of electrically conductive wires stranded around said core Wire with the inner surface of said conductive wires in frictional contact with the serrations on said outer surface of the core wire.

2. In a composite cable for conducting electricity, a

core wire having relatively shallow and rounded serrations in its outer surface along the entire length thereof, a galvanized coating over the serrated outer surface of said core wire, and a plurality of electrically conductive wires stranded around said core wire with the inner surface of said conductive wires in frictional contact with the serrations in said outer surface of the core wire.

3. In a composite cable for conducting electricity, a high tensile strength core wire having relatively shallow and rounded serrations along the outer surface thereof, a protective coating of grease over said outer surface. and a plurality of electrically conductive wires stranded around said core wire with the inner surface of said conductive wires in frictional contact with the serrations on the outer surface of the core wire.

4. In a composite cable for conducting electricity, a plurality of high tensile strength core wires having relatively shallow and rounded serrations along the outer surfaces thereof, and a plurality of layers of electrically conductive wires stranded about said core wires with the inner surface of at least some of said electrically conductive wires in frictional contact with the serrations on said outer surface of the corewires.

5. In a composite cable for conducting electricity a steel core wire having relatively shallow and rounded serrations in its outer surface along the entire length thereof, a galvanized coating over the serrated outer surface of said core wire, and a plurality of aluminum wires stranded around said core wire with the inner surface of said aluminum wires in frictional contact with the serrations in the outer surface of said core wire.

6. In a composite cable for conducting electricity, at least one high tensile strength core wire, having relatively shallow and rounded serrations on the outer surface thereof, a galvanized coating over the serinated outer surface of said core wire, a protective grease coating over said galvanized coating, and a plurality of electically conductive wires stranded around said core wire with the inner surface of said conductive wires in frictional contact with said serrated outer surface on the core wire.

7. In a composite cable for conducting electricity, a high tensile strength core wire having a plurality of relatively shallow annular serrations along the outer surface thereof, and a plurality of electrically conductive Wires stranded around said core wire with the inner surface of said conductive wires in frictional contact with the serrated outer surface of the core Wire.

References Cited in the file of this patent FOREIGN PATENTS 344,194 Great Britain Mar. 5, 1931 22,886/29 Australia Oct. 21, 1930 574,926 Great Britain Jan. 25. 1946 

